A widely used type of conductor cable comprises a film of suitable insulating plastic, such as polyethylene terephthalate having flat ribbon-like conductors thereon in side-by-side relationship. The conductors are contained in the cable among most of its length, but the insulation is stripped from an end portion of the cable on one surface to expose the conductors when it is necessary to connect the cable conductors to further conductors.
Several types of electrical connectors are available for flat conductor cables as shown, for example, in U.S. Pat. Nos. 4,181,386, 3,629,787, and 3,989,336. All of these patents show connectors for connecting flat cable conductors to conductors on a circuit board or the like. U.S. Pat. No. 4,181,386 shows a relatively simple clip of suitable resilient metal, such as spring steel, which is mounted on the circuit board in straddling relationship to the circuit board conductors so that the cable can be inserted between the contact springs of the spring clip and the surface of the circuit board whereby the cable conductors will be pressed against the circuit board conductors. The connector shown in U.S. Pat. No. 4,181,386 is of the zero insertion force type in that the contact springs can be disengaged from the surface of the circuit board to permit insertion of the cable under zero insertion force conditions.
U.S. Pat. Nos. 3,629,787 and 3,989,336 both show connectors comprising plastic housings which contain individual contact terminals. When the cable is inserted into the housing, the spring portions of the contact terminals engage the cable and press the cable conductors either against circuit board conductors, as in U.S. Pat. No. 3,629,787, or against contact portions of the terminals in the connector housing as in U.S. Pat. No. 3,989,336. U.S. Pat. No. 3,629,787 is not of the zero insertion force type and when the cable is inserted, the leading edge of the cable must transmit the forces required to deflect the contact springs so that the cable can enter the connector. Since the cable itself is extremely flexible, it is sometimes difficult to insert the cable because of its tendency to buckle under a relatively low compressive load. U.S. Pat. No. 3,989,336 overcomes this buckling problem by providing a separate clamping member on the connector housing which is normally in engagement with the contact springs and which imposes an external force on the contact springs of the terminals. When the cable is to be inserted, the clamping member is moved away from the terminals so that they no longer are capable of exerting contact forces and the cable can then be inserted under zero insertion force conditions or very low insertion force conditions. After insertion, the clamping member is moved to its operative position in which it presses the contact springs of the terminals against the cable conductors.
The connector shown in U.S. Pat. No. 3,989,336 overcomes the problem of inserting the highly flexible cable into the connector but it requires a relatively complex housing having a separate clamping means integral therewith. Furthermore, if this separate clamping means should become disengaged or inoperative while the connector is in service, the contact forces would be reduced and contact might be lost with the conductors in the cable.
The present invention is directed to the achievement of a multi-contact electrical connector for flat flexible cable which has the advantage of requiring a relatively low level insertion force when the cable is inserted, but it does not require a separate force applying means on the connector housing or any of the other features which are usually associated with zero insertion force connectors, that is features which permit the contact terminals to be displaced away from their normal zones or positions to permit insertion of the cable.
A connector in accordance with the invention comprises a relatively simple insulating housing of molded thermoplastic having a cable receiving face and having a trough-like cable receiving opening extending into the cable receiving face. A plurality of electrical contact terminals are mounted in the opening in side-by-side spaced-apart relationship at locations such that upon insertion of the cable into the opening, each of the terminals will engage one of the conductors on the cable. The contact terminals each have a spring means having a contact portion so that when the cable is inserted, the spring means is deflected by the leading edge of the cable and when insertion is complete, the contact portion will be resiliently held against the conductor on the cable by the spring means. The contact portions of the terminals in the connector housing are arranged in a plurality of rows, for example, the first row comprising the contact portions of every third terminal in the housing, is located adjacent to the cable receiving face so that when the cable is inserted, the leading edge of the cable will first encounter the spring means of this first row of terminals. The second row of contact portions is made up also of every third terminal and this row is located inwardly from the first row and a third row, when provided, is located inwardly from the second row. The leading edge of the cable thus encounters the contact portions of the terminals sequentially, rather than encountering all of the contact portions simultaneously. As a result, the insertion force required to fully insert the cable is initially relatively low, since the cable encounters only a third of the total number of terminals in the housing. Upon further insertion, the cable encounters the second row of terminals and the insertion force must therefore be increased, however, at this stage the contact terminals in the first row will be holding portions of the cable and will thereby discourage buckling of the cable. When the cable encounters the third row of terminals, the insertion force must be further increased to overcome the contact spring means of the third row of terminals but at this stage, the cable will be clamped by the contact portions by the terminals in the first row and the second row. Overall, the operation of inserting the cable into the housing is greatly facilitated and the technician is thereby encouraged to insert the cable properly into the connector housing to ensure effective contact with all of the conductors in the cable.